An abdominal aortic aneurysm is a pathological condition in which a part of the abdominal aorta becomes abnormally enlarged. This happens when a part of the aortic wall is weak. A ruptured aneurysm leads to severe internal bleeding and is, worldwide, a major cause of death. AAA develops slowly over years and most AAAs remain undiagnosed as this condition does not have specific symptoms. It is usually diagnosed when a person is screened, by ultrasound or CT scan for instance, for some other complaint. Once diagnosed, the patient has to be monitored periodically, say, every six months, using ultrasound or CT scans. Surgical intervention is prescribed when the aneurysm reaches a size at which there is a high risk of rupture. However, the patient cannot be monitored frequently enough to completely prevent a rupture as evidenced by the fact that a large number of ruptured AAAs occur in patients with previously diagnosed AAAs and are being monitored.
U.S. Pat. No. 6,921,367 B2 discloses a device for the diagnosis and management of peripheral vascular disease. It suggests that in addition to peripheral vascular disease, other diseases, such as abdominal aortic aneurysm, can be diagnosed and managed. It suggests further that changes in pulse wave velocity and waveform can be followed for years if desired. It describes a circuit schematic of the invention comprising a photoplethysmogram sensor. Two emitters and a detector are positioned adjacent the tissue being measured, such as a finger. In another embodiment, the photoplethysmogram sensor is combined with an ECG amplifier.
The article “Effect of an Abdominal Aortic Aneurysm on Wave Reflection in the Aorta” by Abigail Swillens et al., IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 55, NO. 5, MAY 2008, pp. 1602-1611, discloses that with AAA, pronounced reflections were present in the pressure and flow waveforms. Wave intensity analysis confirmed the presence of a backward expansion wave caused by sudden expansion of the aorta; this was absent without AAA. From a parameter study, it is clear that the impact of the AAA and the generation of the backward expansion wave augment with the increasing size of the AAA. The presence of AAA significantly alters wave reflection and hemodynamics in the aorta, with apparently measurable effects in humans. If this disturbance were measurable at easily accessible arteries, this might offer opportunities for assessing rupture risk and developing new noninvasive detection methods.